Water → 4-(Dimethylamino)piperidine dihydrochloride

After adding 10% palladium-carbon (2.0 g) to a solution of the crude 4-dimethylamino-1-benzylpiperidine dihydrochloride (30.0 g) in 2-propanol (300 ml)-water (300 ml), the mixture was stirred for 22 hours at room temperature under a hydrogen atmosphere. The catalyst was filtered and washed with 2-propanol. The filtrate was then concentrated. The obtained crystals were suspended in ethanol (50 ml). They were then diluted with diethyl ether (50 ml). The crystals were subsequently filtered and washed with methanol (10 ml). They were then subjected to aeration drying to provide the title compound (16.4 g) as colorless crystals.